Boston – For elderly people who suffer bouts of depression, drugs work surprisingly better than psychotherapy at keeping those black spells from returning, suggests the longest study ever in patients so old.

The findings from the two- year study may encourage some doctors to prescribe antidepressants for longer periods, perhaps even for life, in patients who have been depressed.

“It’s a good idea for you to continue to take the medication indefinitely, just as you take your blood pressure medication or diabetes medication,” said psychiatrist Dr. Charles Reynolds at the University of Pittsburgh, who led the study. “It’s a very new approach.”

Backed by the National Institutes of Health, the study responds to a rising trend to prescribe medicine not just to treat depression, but also to keep it from coming back. Results were published today in the New England Journal of Medicine.

Depression is estimated to occur in 3 percent to 5 percent of elderly people and it returns more than half the time within three years.

Psychotherapy, exercise and socializing are viewed as effective long-term shields, since they change behavior.

Yet psychotherapy did little in this study.

Many psychiatrists continue to believe in psychotherapy, even in some very old patients. Psychiatrists suggest that some patients in this study had undergone biological changes in their brains with aging and lost some mental capabilities, making them benefit more from drugs and less from talking therapy.

Also, the psychotherapy in this study was given only once a month for 45 minutes.

The two-year study monitored 116 people ages 70 and above after they recovered from an episode of depression. They were then randomly assigned to take an anti-depression drug, the drug plus psychotherapy, psychotherapy with dummy pills, or dummy pills alone.

Just over a third relapsed into depression with drugs, whether they got psychotherapy or not. More than two-thirds did with psychotherapy and dummy pills, and slightly less with dummy pills alone.

Though the numbers are small, experts view them as significant because it is difficult to recruit elderly volunteers for such research.

Several psychiatrists said the findings probably apply to a range of depression drugs, not just the paroxetine used in this study. They said that it’s unclear just how long depressed patients may need drugs but that they should be monitored and get some form of therapy for years afterward.

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